Makefile: Do not install built-ins

MSYS does not support file system links and we do not want to have copies
that bloat the installation.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
MinGW: Use MakeMaker to build the Perl libraries

This way the libraries get properly installed into the "site_perl"
directory and we just have to move them out of the "mingw" directory.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
MinGW: Fix stat definitions to work with MinGW runtime version 4.0

For an overview of changes in mingwrt-4.0 see:

    http://sourceforge.net/p/mingw/mingw-org-wsl/ci/4.0.0/tree/NEWS

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
git-compat-util: Avoid strcasecmp() being inlined

This is necessary so that read_mailmap() can obtain a pointer to the
function.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
Windows: Do not redefine _WIN32_WINNT

With MinGW runtime version 4.0 this interferes with the previous definition
from sdkddkver.h.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>